Microstructure Evolution Of Thin Films Research Articles

Critical issues in thin film microstructure development

Physical vapor deposition techniques are presently being used to deposit elemental thin films or multicomponent thin films of novel materials like superconductors, oxides, dielectrics, etc. The microstructure development of these films, especially grain growth processes are particularly important for optimization of their electrical properties. In this paper, we focus on two critical issues related to microstructural evolution in thin films: (i) modeling of microstructural evolution during vapor deposition, and (ii) anisotropic grain growth during post deposition annealing in non-cubic systems. One of the key issues in non-cubic oxide systems, especially in high-Tc superconductors, is the anisotropic nature of growth which gives rise to oriented films on lattice mismatched or amorphous substrates. The factors affecting grain growth in non-cubic systems which lead to textured film are discussed in detail. An overview is also presented on the new developments in the modeling of materials synthesis by physical vapor deposition techniques. It is suggested that there is a strong need to formulate theoretical and computational methodologies which bridge both continuum and atomistic descriptions. The concept of “closed” and “open” thermodynamic systems to classify a broad range of microstructural evolution issues in the deposition of thin films is introduced.

Simulation of thin film grain structures—II. Abnormal grain growth

A computer simulation of grain growth in two dimensions has been used to model microstructural evolution in thin films. In a companion paper we have simulated the stagnation of grain-growth due to grain-boundary grooving at the free surface of the film. In this paper we model the effect of driving force variations (due to variations of the free-surface energy among different crystals) on the origination and propagation of abnormal or secondary grain growth. The simulation produces an estimate for the magnitude of the driving force which is required to produce abnormal grain growth. The simulation also indicates that a key requirement for classic abnormal grain growth behavior is that a majority of the grains have free-surface energies which differ very little from each other.

Grain Growth in Thin Films

in the average crystal orientation and can even result in epitaxial films. It is therefore not surprising that grain growth can profoundly affect the mechanical, electrical, and chemical properties of thin films. In this article the mechanisms and modes of grain growth in thin films will be reviewed. The focus will be on those factors that lead to the evolution of grain orientations as well as grain si zes. Spec ific attention will also be gi ven to those factors that allow control of microstructural evolution in thin films.

Simulation of thin film grain structures—I. Grain growth stagnation

A computer simulation of grain growth in two dimensions has been used to model microstructural evolution in thin films. In particular, we have modelled the effects of grain-boundary grooving at the free surface of a film by introducing a stagnation condition on grain-boundary migration. This stagnation results in a lognormal grain-size distribution, which is similar to experimentally observed distributions.

Low Energy Ion Bombardment and Microstructural Evolution in Thin Films

ABSTRACTA new approach to modeling the evolution of islands in thin films by growth and coarsening during ion bombardment is described. Solution of a continuity equation and matter conservation relation, coupled with interface-limited and diffusion-limited rate laws for island growth and coarsening allows the kinetics of island evolution to be modeled. Results from the model indicate distinct kinetic paths for island evolution during ion bombardment as a result of growth, enhanced diffusion, island dissociation and monomer sputtering.

Computer simulation of microstructural evolution in thin films

The nature of the microstructure of a thin film strongly affects its functionality in electronic applications. For example, the rate of electromigration-induced failure is a function not only of the grain size in an interconnect line, but also of the width and shape of the grain size distribution. We are developing techniques which allow prediction of the relationships between the conditions for thin film processing and the topology and geometry of resulting grain structures. We have simulated two-dimensional microstructural evolution by determining the location of grain boundaries after nucleation and growth of crystalline domains. We have allowed for nucleation under a variety of conditions including constant nucleation rates, decreasing nucleation rates and instantaneous saturation of nucleation sites. We have also allowed for increasing and decreasing growth rates which depend in various ways on the domain size. We have simulated grain growth in two-dimensional structures by allowing boundary and triple point motion in order to reduce the total grain boundary area. The rate and nature of the initial stages of grain growth are strongly affected by the conditions for nucleation and growth. Eventually, however, grain growth appears to proceed as expected from analytical treatments.

Development and evolution of thin film microstructures: A Monte Carlo approach

A computer simulation procedure based on the Monte Carlo algorithm has been developed to study the thin film microstructure evolution in the Zone II regime. This is accomplished by letting the grain boundary movement on the film surface couple with the microstructure in the interior of the film. The grains when viewed in cross-section are found to reach a limiting size at which point all grain boundary motion ceases despite the presence of capillarity driving force. This results in a columnar morphology for the thin film. The cross-sectional size distribution function is found to be approximately log-normal in shape. The introduction of anisotropic solid-vapor interfacial energy is found to induce abnormal grain growth at the expense of the normal grain which has a relatively higher solid-vapor energy. An analytical model is proposed in which the formation of the columnar structure is explained in terms of the grain boundary drag at the growing interface due to sub-surface boundaries.